In the present study, the dried biomass of Ulva faciata was subjected to different chemical pretreatments at different incubation periods to find the most appropriate method of cell disruption that increase extracted lipid, fatty acids and improve the quality of the produced biodiesel with low cost. These pretreatments were as follows: acid (HCl and 1% H₂SO₄) for 1, 2, and 3 hrs, alkaline (NaOH, pH=12) for 1, 2, and 3hrs and osmotic shock (36% solution of NaCl) for 24, 48 and 72 hrs. The control was kept at optimum conditions without pretreatment: 60 min extraction time, 55^oC, shaking speed at 250 rpm, < 0.16 mm particle size with 25:1 v/w solvent to solid ratio, using chloroform: methanol: H₂O (2: 2: 1) solvent mixture. The results showed that all chemical pretreatments have a significant effect on total fatty acids yield, where ÓFA was 1148.94µgg^-1 dried alga without any treatment, while using acid pretreatment with HCl (pH=2) for an optimum time period (1h) resulted in an about 2.9-fold increase in ÓFA yield, while it resulted in an about 2.4-fold increase in ÓFA yield when pretreated with 1% H₂SO₄ for an optimum time period (2h). On the other hand, alkaline pretreatment with NaOH (pH=12) for optimum incubation period (2h), resulted in an about 2.84-fold increase in ÓFA yield, while the osmotic shock of NaCl for 72h, gave the about 3-fold increase, but it needs longer incubation periods, which cause time-wasting. The produced biodiesel after all chemical pretreatments had a high quality and its properties complied with the ASTM D6751 and EN14214 standards, except in the case of 1% H₂SO₄ and NaOH; they were slightly higher than the limit of EN14214 standard. These results were confirmed statistically; where it was observed that all chemical pretreatments had a high significant effect on fatty acids yield and on all properties of the produced biodiesel.